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Debt (Long-term Debt) (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019	Nov. 15, 2019	Jun. 27, 2017	Jun. 10, 2014
Debt Instrument [Line Items]
Less: Unamortized discount	$ 120,910	$ 139,981
Deferred issuance costs	12,453	14,058
Total long-term debt	1,469,051	1,448,461
Less: current portion	393,980	385,532
Total long-term debt, less current portion	1,075,071	1,062,929
Senior Notes \| 6.0% Senior Notes
Debt Instrument [Line Items]
Stated interest rate				6.00%
Total Notes	650,000	650,000
Convertible Debt
Debt Instrument [Line Items]
Total Notes	1,602,414	1,602,500
Convertible Debt \| 3.25% Convertible Notes
Debt Instrument [Line Items]
Stated interest rate					3.25%
Total Notes	402,414	402,500
Convertible Debt \| 1.75% Convertible Notes
Debt Instrument [Line Items]
Stated interest rate			1.75%
Total Notes	$ 550,000	$ 550,000
Deferred issuance costs			$ 2,800